In a reciprocating compressor driven by a linear motor, the gas compression and gas suction operations are performed by axial movements of each piston reciprocating inside a cylinder, which is closed by a cylinder head and mounted inside a hermetic shell, in the cylinder head being positioned the discharge and the suction valves, which regulate the admission and discharge of gas in relation to the cylinder. The piston is driven by an actuating means, which carries magnetic components operatively associated with a linear motor affixed to the shell of the compressor.
In some known constructions, each piston-actuating means assembly is connected to a resonant spring affixed to the hermetic shell of the compressor, in order to operate as a guide for the axial displacement of the piston and to make the whole assembly actuate resonantly in a predetermined frequency, allowing the linear motor to be adequately dimensioned for continuously transferring energy to the compressor during operation of the latter.
In a known construction, two helical springs are mounted under compression against the actuating means on each side thereof. The piston, the actuating means, and the magnetic component form the resonant assembly of the compressor, which assembly is driven by the linear motor and has the function of developing a reciprocating linear movement, making the movement of the piston inside the cylinder exert compression on the gas admitted by the suction valve, until said gas is discharged to the high pressure side through the discharge valve.
Helical springs under compression, independently of the shape of the last coil that will form the contact region with the piston, have the characteristic of promoting a contact force with an uneven distribution along a determined contact circumferential extension, with a concentration of compressive force in the region where the last coil begins contacting the piston.
According to calculations, 85% of the reaction force is applied to the first 10 degrees of the contact region (indicated by the angle β in FIG. 2), the remainder (15%) of the reaction force being distributed along the complement of the circumferential extension of the contact region. As a consequence, the piston is submitted, mainly when displaced from its resting position, to a momentum which causes a misaligned movement of said piston in relation to the cylinder, resulting in wears that decrease the life of the compressor and increase the occurrences of noise and vibration during operation thereof.
This effect is noted while each helical spring is operating as a spring in the assembly, since the compressive force on the actuating means is only equally distributed along the contact surface in the moment in which said helical spring achieves a solid length with all the coils, when said spring begins to act as a block. The occurrence of a momentum is present, although with less intensity, even in the constructions in which the last coil of said helical springs presents part of its extension flat.